The present invention relates to an off-road vehicle and more particularly to a vehicle suitable for use as a grader on soft, low density surfaces, for example snow or loose soil.
A grader attachment for use on a tracked snow vehicle is disclosed in Eskelson et al. U.S. Pat. No. 3,616,557, issued Apr. 18, 1972. That attachment includes a scraper blade across the front of the vehicle and a boom pivotally mounted on the vehicle to extend to the front, beyond the scraper blade. A ski is mounted on the end of the boom to support the boom and the vehicle. In preferred versions of this attachment, the ski is steerable to limit the requirement for skid steering of the vehicle.
The present invention relates to certain improvements in graders for use on soft services.
According to the present invention there is provided a vehicle comprising:
a vehicle body;
two endless drive track assemblies mounted on opposite sides of the body;
an elongate boom mounted on the body and extending in a forwards direction from the body;
a third endless drive track assembly;
a steering mechanism mounting the third endless drive track assembly on the boom, spaced forwardly from the body, for rotation about an upright steering axis; and
drive means for driving each of the drive track assemblies.
The use of a steering, driven track on the boom provides a tractive force pulling the vehicle forwards in the desired direction of travel and positively driving the leading end of the boom in the direction of a turn. This distinguishes from relying on the reactive force of the surface material on a passive keel imbedded in the surface, as in the prior art. The track also provides a degree of packing at the center of the vehicle""s path that can not be achieved with a ski gliding on the surface. This is of particular importance when packing trails with the vehicle. The track also allows the use of the vehicle on surfaces where the friction generated by engagement with a ski would make the ski arrangement unusable.
In preferred embodiments of the vehicle, the vehicle tracks are supported on the vehicle by walking beam suspensions and the boom is fixed to the vehicle. This provides a three point support for the vehicle that maintains vehicle stability and good engagement of the tracks on the surface without resorting to the use of an hydraulic boom control.
For grading purposes, the vehicle has a grader blade across the center of the vehicle and a second blade leading the front track. This provides both grading and packing at the center of the track where prior art tracked vehicles would at most provide a grading action with a scraper blade.
It is preferred that the leading blade have an hydraulic lift system for positioning the blade vertically with respect to the leading track. It is also preferred that the second blade can be angled from side to side to provide a camber on the surface being graded and angled with respect to the direction of travel. This provides full flexibility in grading a surface, including the ability to place soil or snow to one side or other of the vehicle""s path.
The invention will now be described by reference to an exemplary embodiment of the invention. It is to be understood that the invention is not limited to that embodiment but may include many others.